gh.r. gordani

Dealing with the destructive effects of electromagnetic waves requires materials with the ability to lose magnetic and electrical energies. These materials are mainly composed of a magnetic material and an electrically conductive material. In the present research, at first, strontium ferrite nanoparticles doped with manganese and calcium with the formula of SrCo2-X(Mn Ca)X/2Fe16O27 (x=0.0-0.5) were synthesized by co-precipitation method. Then these nanoparticles were composited together with functionalized carbon nanotubes (with a volume ratio of 1 to 5%). X-ray diffraction analysis, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, vibrating sample magnetometer, and vector network analyzer were used to investigate the structural, magnetic, and microwave properties of the samples. The X-ray diffraction pattern results showed that the strontium ferrite phase was formed in all compounds, and there was no evidence of any impurities in the samples. FE-SEM results indicated that the particles completely covered the outer walls of the carbon nanotubes. Magnetometer test results also showed that with an increase in the amount of manganese and calcium cations in strontium ferrite, the saturation magnetization decreased and the coercive force increased. Reflection losses were also at least 30% higher in composite samples than those of in ferrite samples. The highest reflection loss (7.42 dB at a frequency of 1.12 GHz) was observed in the nanocomposite sample containing 5% by volume of carbon nanotubes. However, based on the results, the sample containing 4% by volume of carbon nanotubes had a wider absorption bandwidth compared to other samples.

The goal of this study was the investigation of the structural and magnetic characteristics of MnBi permanent magnets. In this regard, the mechanical milling and annealing processes were used for the synthesis of Mn45Bi50M5 (M= Sb, Ge, B) samples. Based on the results, the best annealing temperature and time for the formation of the highest value of MnBi ferromagnetic phase with optimum magnetic properties (Hc=1750 Oe and Ms= 12 emu/g) were recognized at 325 oC and 24 h, respectively. B, Ge, and Sb elements had a distractive effect on the stabilization of the MnBi ferromagnetic phase. Consequently, the samples containing B, Ge, and Sb showed lower magnetic characteristics in comparison with the Mn50Bi50 stoichiometric sample.